student_age = [21, 25, 21, 23, 22, 20]
print(student_age)
student_age.append(31)
print(student_age)
student_age.extend([29, 33, 30])
print(student_age)
del student_age[0]
# student_age.remove(21)
print(student_age)
student_age.pop(-1)
print(student_age)
index = student_age.index(31)
print(f"元素31在列表中的下标位置：{index}")